Playing a scenario where only one player has an Air plane - in this example Gallabat - Metemma, Italians have a Fiat CR.42 fighter sitting on the runway at the start of game.

What is the situation where the non plane owning player picks up the Air Power card? Does it count as an Air Sortie equivalent, and is therefore of no use to him? If so, is the default - "order one unit of your choice" as with other cards that order some unit that you mave not have?

If Air Rules are in effect, and there is no specific note about Planes, then any player can bring one onto the board if they get an Air Sortie or Air Power card. There are some scenarios, though, where the rules specifically say one of the players cannot use Air Sorties and must discard them immediately.

I think where I went wrong is in making an assumption that one side didn't have access to airplane's. Just because the Axis player stars with a plane on the ground initially, doesn't mean that the Allied player has no 'planes for the entire game.

There was no special rule stating "No Airplanes" for Allied player.

Historically, in the Gallabat-Metemma scenario they had a bunch of old Gladiator Bi-planes and a few really ancient bombers.

I think where I went wrong is in making an assumption that one side didn't have access to airplane's. Just because the Axis player stars with a plane on the ground initially, doesn't mean that the Allied player has no 'planes for the entire game.